This invention relates to seal assemblies for rolling bearings.
In the prior art, one type of seal assembly for rolling bearing has labyrinth seals which are provided on one of the two race rings and closely spaced apart from the other ring by the labyrinth gaps, while another type of seal assembly for the same has seals including seal lips which are equipped on one of the two race rings and slid on the other race ring.
The labyrinth seals of the seal assemblies of the above-said prior art have less efficiency of sealing as a matter of course, so that the lubricants can leak out of the rolling bearings and water and dust etc. can intrude into the bearings from the outside, whereby performance of the rolling bearings will be deteriorated.
On the contrary, the latter type including the seal lips slid on the race ring has high ability of sealing and still allows the race rings of the rolling bearing to provide for the low torque and high speed of rotation. However, obstructions, such as excessiveness of the torque and damages of the seal lips etc., will occur to the rolling bearing, when the temperature at which the rolling bearing is used is abruptly changed (cooled down from a high temperature), because the seal lip portions are always held in contact with the race ring by the needed contacting pressures, though which are low, with the result that the inner pressure of the rolling bearing becomes lower than the outer pressure in the event of the abrupt change of that temperature, by which depressurization the seal lips are more tightly compressed on the sliding contact surfaces of the race ring and vicinities thereof, which results in enlargement of the contacting areas of the seal lips accompanied with the excessiveness of the torque, and, in the worst case, results in the damages of the seal lips. If the seal lips have higher stiffness, the expansion of the contacting areas will be decreased, but, even with the small enlargement of the contacting areas, such impediments as the excess of torque and the damages of seal lips etc. should still arise.
Therefore, in order to permit the passage of air between the insides and outsides of the rolling bearings so as to dissolve the problem of the pressure changes in the rolling bearings, there has been proposed a seal assembly in which the seal lips are formed with airing slots within their sliding contact surfaces (See Japanese Patent Publication No. 44-19641), and there is another seal assembly in which ventilating openings are formed within the external peripheral surface of the seal and throughout the seal lip portions. However, these seal assemblies diminish the ability of sealing in the same way to the labyrinth seals, owing to the slots formed within the sliding contact surfaces of the seal lips or to the openings formed within the external peripheral surface of the seal and throughout the seal lip portions, so that the leakage of the lubricant out of the rolling bearings and the intrusion of water and dust etc. from the outside can occur again, thereby performance of the rolling bearings should be degraded.